The present invention relates to an improved process or method for transferring a coating onto at least one surface of a lens blank which can be implemented in a short period of time without any risk of deformation of the lens blank.
It is a common practice in the art to coat at least one face of an ophthalmic lens with several coatings for imparting to the finished lens additional or improved optical or mechanical properties.
Thus, it is usual practice to coat at least one face of an ophthalmic lens, typically made of an organic glass material, with successively, starting from the face of the lens, an impact resistant coating (impact resistant primer), a scratch resistant coating (hard coat), an anti-reflecting coating and, optionally, a hydrophobic top coat. Other coatings such as polarized coating, photochromic or dying coating may also be applied onto one or both faces of the ophthalmic lens.
Numerous processes and methods have been proposed for coating a face of an ophthalmic lens.
U.S. Pat. No. 4,061,518 discloses a process for fabricating an article having a replicated coating with a durable dielectric overcoat thereon which comprises forming onto an optically polished surface of a master a release layer, a protective coat and a reflective coat, applying a pre-measured amount of an epoxy resin adhesive on a face of a support member of casting, and thereafter transferring the coating from the master to the support member of casting by applying the coating face of the master to the epoxy resin adhesive, curing the epoxy resin adhesive under heat and withdrawing the master. The support member of casting is preferably an aluminium casting. The described method is particularly suited for making mirrors.
WO 99/24243 discloses a method of making a thermoplastic lens by placing a laminated layer/coating having the desired lens characteristics required for the prescription between a preheated lens blank and preheated mold halves and pressing the mold halves toward each other to compress the lens blank and uniformly apply the layer/coating thereon without any creases or cracks therein.
In this method, the lens molds are pressed toward each other and against the lens blank to immediately size down the lens blank and any laminations included therewith to its finished lens size with the desired layer coatings in few minutes. In fact, the lens blank and juxtaposed laminations are compressed at a predetermined programmed rate of speed, whereby the lens blank is compressed and spread out into the mold cavity with a layer/coating uniformally applied thereon.
In order to obtain the required geometry for the final lens, spreading of the blank must be carefully controlled and therefore heating and compression have also to be carefully controlled.
U.S. Pat. No. 5,512,371 discloses a composite plastic optical quality lens, comprising a plastic lens preform of optical quality material, and a cured plastic attached portion that is bonded to said plastic lens preform portion; said cured plastic attached portion having higher scratch resistance, and lower chromatic aberration than said plastic lens preform.
Such a lens is obtained by pouring a lens composition in a molding cavity delimited by a mold part and a lens preform and then curing said lens composition.
According to one preferred embodiment of U.S. Pat. No. 5,512,371, coatings may be provided on the resultant lens by transferring coatings from the mold to the resultant lens.
The purpose of U.S. Pat. No. 5,512,371 is to substantially modify and improve the mechanical properties of the plastic lens preform, generally made of bisphenol A polycarbonate. In particular, properties such as edging and chromatic aberration of the whole resultant lens are supposed to be significantly modified by the cured attached portion. Such results are achievable only for cured attached portions having a thickness globally in the same range or even higher than the thickness of the preform, taking into account that the usual center thickness of the final resultant lens is generally, as known in the art, of more than 1 mm.
If it was not the case, the modifications brought by the cured portion would have no significant effects on the properties of the composite lens such as chromatic aberration and edging.
WO 93/21010 also relating to the manufacture of composite lenses gives a minimum thickness for the preform.: 100 microns, with typical thickness of 0.5 to 1.5 mm.
In general, it is difficult to manufacture and handle preforms that are less than 500 microns thickness.
Based on the above elements, it is clear that thicknesses for the cured attached portion of U.S. Pat. No. 5,512,371, even if not specifically mentioned, are typically around 0.5 mm or above.
According to the method of manufacture described in U.S. Pat. No. 5,512,371, a resin is poured in a mold and a lens polycarbonate preform is placed on the top of the resin filled mold, slight pressure is applied to squeeze out excess resin until a carrier of sufficient thickness is obtained.
The assembly lens/preform/mold part is held together with the capillary action of the resin material and the weight of the lens preform.
WO 97/35216 discloses a process for transferring a multilayer coating onto the surfaces of a lens which comprises:                providing a thin polymeric film substrate which is flexible and extensible and having one face coated with the transferable multilayer coating;        placing the coated film substrate in an apparatus including a film deforming member;        disposing a drop of an adhesive between the film substrate and a lens surface;        urging the film into conforming engagement with a surface of the lens; and        curing to adhere the multilayer coating on the lens surface.        
In this process, the film substrate is stretched to conform to the surface of the lens, thereby stretching the multilayer coating. Stretching shall in fact be avoided because it entails a high risk of tearing and/or cracking the layers of the multilayer coating, in particular mineral layers such as conventional antireflective layers.